The present invention relates to improvements to a generally flat side by side cascade impactor, and includes apparatus for testing the integrity of seals, as well as the pressure drop across impactor nozzles or orifice to check the condition of the impactor nozzles. The cascade impactor also includes improvements in mounting and operational features.
In the prior art, it has been known to size classify and collect aerosol particles onto impactor plates. When series arranged nozzles are used, it is desirable to determine the condition of the nozzles, and whether or not they are becoming plugged or worn. This can be done by determining the pressure drop across nozzles, and in a cascade impactor, checking the pressure drop from the inlet to the outlet for total flow analysis is desirable.
Cascade impactors are widely used for size distribution analysis of aerosol particles, for example, for checking for air pollutants, and for also analyzing the chemical makeup of particles in the atmosphere. Size distribution is important, particularly in the drug delivery industry, where a metered dose of an inhaled drug delivered in aerosol form is tested for particle distribution. In such a cascade impactor it is important to insure the consistency of the test, which is related directly to the size of the nozzle or orifice or openings. The total nozzle or orifice opening in a nozzle or orifice plate can be analyzed by determining the pressure drop at a standard flow rate.
The present invention relates to a drug metered dose or dry powder inhaler cascade impactor that has a separate test cover that can be used for determining the pressure drop across individual impactor nozzles, to in turn determine the condition of the nozzles and whether or not there is any plugging, wear or other abnormality. The separate test cover fits in place on the impactor, and when a standard flow rate of a gas, such as air, is passed through the impactor, the pressure drop across the individual nozzles can be sensed, and the total pressure drop also can be sensed.
The pressure inputs are provided to a set of pressure transducers, that provide outputs indicating pressure in each of the passageways on opposite sides of each nozzle plate, and thus the pressure drop across one or more of the nozzle plates or total pressure drop can be determined easily. The pressure drop can be used for determining an accurate total flow rate, which is important in the determination of particle distribution, particularly in dry powder inhalers.
The test cover that is utilized can also be used for applying a vacuum to the system utilizing a vacuum source, which indicates the integrity of the seals on the individual impaction chambers used in the cascade impactor.
Mechanical improvements shown include the placing of the hinges and latch part devices that have cavities on the base plate only, so that the cover, which has passageways for conducting samples can be washed fully between sample runs in automatic washers. The base that is used is not washed each time, and the parts that have hard to clean bores or recesses located on the base.
Additionally, a unique latch actuator is utilized that will release the latches using a cam arrangement. Further, the cover is made so it can be quickly removed and replaced. The hinges are constructed so the cover will not close if the cover is not properly positioned relative to the base.
A method of milling undercut seal grooves in a seal carrying plate, which are within the boundaries of the plate and do not open to edges where a tool can be introduced is shown. Also, a final filter for the exhaust air is disclosed.